Re: Sharpening Cowry-X

Sun Jun 02, 2013 6:44 pm

Almost forgot!

In the steel we are talking about the Chromium carbides have a different overall effect compared to a vanadium carbide. They will sharpen on waterstones or even natural stones they just have a consistently slow pace at which the metal is removed, even if diamond hones are used.

Steels with high percentages of vanadium carbides is where the problems become more apparent because they are much harder carbides.

Re: Sharpening Cowry-X

Sun Jun 02, 2013 7:14 pm

ken123 wrote:Not meaning to pile on Shaun, and I've had some strange theories too, but I'm not quite buying this simple physics. The pushing and pulling isn't pushing carbides in or out as the forces exerted are not perpendicular to the surface but rather more parallel so equally likely to dislodge carbides in either direction.

Shaun, do you have some references regarding 1st gen powdered steels and carbide fallout and fine grain carbon ...chromium.? Always here to learn.

---Ken

Ken, you've already talked WITH me about this IN PERSON

It's common knowledge that high-chromium steel produces larger carbides. I always have stainless steels lose their high-refinement faster than carbons. You can strop carbons back better than stainless because there is less chromium. High-chromium content and bad heat treatment are the 2 biggest causes of carbide growth.

It's much easier to roll an edge using edge trailing, why do you think Murray Carter took so much flack? After much practice, a few of our BEST sharpeners (Tom, Mike) could pull off his method of using only edge trailing to finish. The conversation is big and deep regarding substrates and steels, etc, but the fact is that people have less success that way, and will have even less on high-chrome steels.

The original poster never replied back or tried edge leading strokes instead, so it's up in the air. I'm here to learn as well, not get ganged up on for requesting someone try something.

Re: Sharpening Cowry-X

My oh my did my blood just boil. I'm in a lot of pain with a sprained wrist right now (fought with a shark last week) (really)....

Jason, I'm seeing a lot of light in your conversation after reading a few more times, and feel like there's a little more than meets the eye here. No denying your experience with powdered metals.

Carbide fallout only really happens on steels that weren't heat treated right, or have HUGE carbides.

Powdered metals are not easy to get heat treat perfect, they require soaks above 2,000 degrees and can vary a couple hundred depending on what you are trying to do (if I remember correctly).. so nailing the heat treat on an exotic steel is not easy. Maybe that's where this whole powdered metal and carbide fallout conversation began. ? That's food for thought IMO. Fine grain steel is still fine grain steel no matter the composition, and won't suffer from fallout. Maybe his knife has bad heat treat.

When Shun originally launched the Elite line (SG-2) the heat treat was so difficult for them that they stopped making them altogether. The new Reserve line uses it now, as well as Mr. Tanaka's Ironwood line (which now that I think about it, I just repaired a petty last week, and it took a 4K edge like no one's business, much better than the Elite santoku I have, totally different experience)

Re: Sharpening Cowry-X

Sun Jun 02, 2013 8:16 pm

Shaun,

No offense intended. I was simply setting the stage for you to expand on what you were saying. I'm going to bow out of this thread so I am not further offending you as that was not my intent at all. I'd also encourage the original poster to try multiple approaches.

Re: Sharpening Cowry-X

Sun Jun 02, 2013 8:48 pm

Sorry, but it seemed as though you had forgotten about some of the conversations we've had about cutting carbides, fallout, and whatnot. I've done so much reading over all of this and never really spit a lot of it back out to other people. Those sources you linked are great.

I should have explained everything a little better first. But, I think we have scratched the surface on the theory of fallout again, that goes deeper than most people think of, which was exactly where Jason was taking the conversation. Substrate and Abrasive vs. Carbide-type (vanadium, chromium)

It was theorized that an abrasive harder than a carbide will cut that carbide much easier without dislodging it from the surrounding steel matrix, which is why CBN and Diamond work so well even on exotic steels at higher refinements.

There is the part of "getting the job done" before human error destroys the edge. Stropping over, and over, and over, freehanded, you are bound to go over on the angle enough time to fatigue the edge, it's inevitable. A razor is different because it has a built in angle guide.

Some steels don't do good past 2,000 grit. This would indicate it has large carbides, or possible bad heat treat. Bad heat treat will make an edge fail very fast, but you can still sometimes get them sharp. A knife doesn't necessarily need to be hard to get refined, but it does to take an acute angle.

So, if you are sharpening around 15 or 20 degrees (aka, nothing too steep) and it's not taking 6k refinement, then how is it doing at the 1k mark? If you can't get a 1k edge on it then there are other things to talk about.

Re: Sharpening Cowry-X

Sun Jun 02, 2013 9:51 pm

Edge stability: the ability for a cutting edge to resist deformation.

Edge stability is usually a combined factor of hardness and toughness, but this does not always mean the edge refinement can be taken to the max. One must cut with a given type of steel until the edge no longer cuts, manila rope is good for this and show how the steel being used reacts to abrasive wear. It will also give you a idea of what level of refinement is best for the steel.

Steels with lots of Chromium carbides (CPM-154, ZDP, cowry-x, ect) will take a very fine edge and hold it for much longer than a steel with high amounts of vanadium carbides (S30V, S90V, ect) due to the rate at which the steel matrix and carbides wear. The Chromium carbides tend to wear with the matrix whereas vanadium carbides dont and stick out of the matrix that is abraiding around them until that matrix of steel and the carbides are worn away. You could say they fall out but on the scale we are speaking of the matrix is "falling out" too.

Vanadium carbides are over 80hrc so pretty much everything around them can be considered soft.

The carbide size is almost a moot point too as PM steels have a very fine grain structure and very small carbides. Compared to something like D2 which has very large and random sized carbides.

As for the refinement of a cutting edge, when large amounts of vanadium carbides are present it would be best to stick with a finishing grit below 1000. It's been proven time and again that coarser is better with these steels and that's something I even have a hard time swallowing but its true.

Refinement of a softer metal with lower alloy content (aka henckles) has a similar thought but relates back to edge stability or lack of. To make up for this lack of edge stability a coarser edge is used. Basically its thicker at the apex so its harder to deform.

Re: Sharpening Cowry-X

Mon Jun 03, 2013 4:06 am

My apologies for not hopping immediately back in. It looks like I missed quite a bit of debate!

I decided to resolve the magnification issue before moving forward. Amazon has a Peak 22x loupe with illuminator headed my way (at a too-good-to-be-true price for a piece of that quality), but that won't be here until mid-week.

Of course, that didn't stop me.

Before reading the back-and-forth here, I decided to see what leading and training strokes would do. Well, past hopefully making sharpening a bit faster...

On getting the knife onto my 2k and not immediately feeling the edge angle, I decided to back up a step and clean up several years of what might have been mis-sharpening on my part and re-set the bevels on my Shapton Glass Stone 500. The included angle on the road is ~5* (~2 mm in 45 mm, each side) and the edge is just a hair more (probably around 8-10* total included), so the angle is still pretty steep on these. Moving through the 2k I had a decent edge on it, as well as off the 6k. I won't say a "great" edge, but I will say that the combination of resetting the bevels as well as leading and trailing strokes seem to have improved the overall situation. Sorry, I hadn't read all this so I can't call it a "controlled test" of the leading/trailing approach.

I suspect that the edge is too acute for my skills to get a "great" edge, so will be backing off a bit to see how that goes once I get the new magnifier.

I want to look at the edge before I do and along the wat for a couple of reasons:

I see a couple bumps in the edge, on one side only, when the light shines off them. The only way I can explain them is they are like a couple tiny, polished zits. I want to better understand what they are before I grind them off again.

The other is that when sharpening the knife, I would occasionally get very tiny, very sharp pieces in the swarf, definitely on the 2k and even occasionally on the 6k. I suspect that the edge is failing somehow and I'd like to better understand what is happening there as well.

I expect the loupe later this week, but I might be distracted by a FedEx box from CKTG that has a Konosuke in it that should be delivered tomorrow. Even with new toys, I will definitely check in when I have more experiences. These have been knives that, when sharp, are among my favorites both in performance, as well as just they way they feel in your hand. The balance is sweet. The handles are very comfortable for my hand, don't slip, and the finger relief on the santoku just makes me smile.

If these photos ring a bell in someone's memory with more information on these knives (or your kanji skills are better than mine), that would be welcome as well.

The 160 mm santoku is 2.65 mm thick and 45 mm tall. The 150 mm petty is 2.2 mm thick and 29 mm high. Only the santoku has the finger relief in the heel (right-handed side only). Both appear to be of sanmai construction.

Any pointers/links as to how to better at knife photography?

If anyone of you "greens" wants to "play" with these knives to see how they support or refute ideas on sharpening these alloys, I'd be happy to cover postage.